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ADD, SUBTRACT, MULTIPLY, and DIVIDE


\begin{command}
\item[\textbf{Form:}ADD dest {[other]} {[CONST=c]} {[BOX=B]} {[...
...ision by the mean of 'other', preserving the
mean of the source.}
\end{command}
These commands perform all arithmetic between images and spectra. There are three ways to use these commands.

Operations between two images or two spectra:

In this form, the command word is followed by the numbers of the buffers holding the images. Examples are
\begin{example}
\item[ADD 1 2\hfill]{Add image in buffer 2 to image in buffer 1...
...ACT 3 4\hfill]{Subtract image in buffer 4 from image in buffer 3.}
\end{example}
Note that the first buffer listed is the one modified by the operation.

The FLAT word is used in the DIVIDE command to re-scale the division by the mean of the second image, thus preserving the mean of the first buffer. This is typically used when dividing raw images by a flat field. NOTE: The mean of the second image must have previously been calculated by the MN command!

Operations between images and constants:

In this form, there is only one buffer specification on the command line. The word CONST= (or C=) is used to specify the constant to be used.
\begin{example}
\item[ADD 2 CONST=9.5\hfill]{Adds 9.5 to every pixel in buffer ...
...m[DIVIDE 3 CONST=10/3.1415\hfill]{ Divides buffer 3 by 10/3.14159}
\end{example}

Combined image and constant operations:

The first two forms of these commands may be combined, thus allowing you to simultaneously operate on two images and a constant.
\begin{example}
\item[ADD 2 3 CONST=5\hfill]{Adds buffers 3 to 2, then adds 5.0...
... by buffer J
(J a variable), then multiplies the result by 0.01.}
\end{example}

Remarks:

In two-image arithmetic, only those pixels common to the two images are changed by the operation. The size of the destination image is not changed by the operation. The DR= and DC= keywords only apply to two-image arithmetic and specify row and column offsets between the two images. The sense of the shift is shown in the following example: dest(C+DC,R+DR) = dest(C+DC,R+DR) + other(C,R).

BOX limits the operation to those pixels in the destination image which are in the specified box.


next up previous index
Next: SQRT: Square Root of Up: Image Arithmetic Previous: Introduction to Image Arithmetic   Index
Jon Holtzman 2002-02-13